Studies on ticks of veterinary importance in Nigeria. VI. Comparisons of oviposition and the hatching of eggs of Hyalomma species.

Fully engorged Hyalomma spp. in Nigeria oviposited greater numbers of eggs than those partially engorged. Hyalomma impressum was a more prolific egg layer than H. rufipes, H. impeltatum and H. truncatum. The variations in the egg output as well as the recognizable peaks in the number of eggs during oviposition were described for each species. No species of Hyalomma below the engorged weight of 0.2 g oviposited; oviposition started with ticks of weight 0.3 g. Eggs produced by ticks weighing below 0.3 g did not hatch; the highest percent egg eclosion occurred with ticks of weight 0.6 g (H. rufipes) and 0.7 g (other Hyalomma species). The pre-oviposition, oviposition and eclosion periods were shortened when eggs were laid and incubated at high temperatures, although the number of oviposited eggs did not increase significantly. At the standard temperature of 24 degrees C, the longest eclosion period was seen in the eggs of H. rufipes (41 days) while those of H. truncatum, H. impressum and H. impeltatum were similar to each other (29 days). Only eggs of H. rufipes hatched at an incubation temperature of 15 degrees C. Eggs of Hyalomma species laid at the same time hatched over a 2--4 day period, except at 15 degrees C when the hatching period of H. rufipes lasted 10 days. The eclosion period was longest in the earlier ovipositions and shorter in the later ones. It is suggested that some intrauterine larval development might have started in the eggs before they were released at a later oviposition period. The percentage mortality of eggs at various temperatures showed that eggs of H. rufipes were more tolerant of low temperatures than those of H. impressum, H. truncatum and H. impeltatum, while the eggs of the latter 3 species were more tolerant of high temperatures than those of H. rufipes. The relevance of these results of the distribution and abundance of the Hyalomma species in Nigeria was discussed.